Moulds (or mildew) are fungi. Fungi are neither plant nor animal but, since 1969, have their own kingdom.
The fungi kingdom includes such wonderful organisms as the delicious edible mushrooms, the makers of the “miracle drug” penicillin and the yeast that makes our bread rise and our fine wines ferment. Biologically, all fungi have defined cell walls, lack chlorophyll and reproduce by means of spores.
Approximately 100,000 species of fungi have been described and it is estimated that there are at least that many waiting to be discovered. The vast majority of fungi feed on dead or decaying organic matter – they are one of the principle agents responsible for the natural recycling of dead plant and animal life.
Mould begins life as a spore (comparable to seeds in the plant kingdom). Spores are minuscule and are ever present in the air around us. Because of their size ranging from 3-40 microns (human hair is 100-150 microns), they are literally everywhere. In very humid air, the concentration of spores is much higher. Because of their tiny size, they are carried by air currents and only settle on surfaces in very still air. They may stay dormant for long periods of time, waiting for favorable conditions to germinate.
There are four critical requirements for mould growth – available mould spores, available mould food (organic substance), appropriate temperatures and considerable moisture.
Once germinated, the mould produces string-like filaments known as hyphae. This is the growing stage of the mould. When many hyphae come together, the mass is known as mycelium, the visible part of the mould which can produce and release spores into the air to start new colonies. In contrast, fungi that can adopt a single celled growth habit are called yeasts.
The good and bad aspects of moulds
Moulds cause biodegradation of natural materials, which can be unwanted when it becomes food spoilage or damage to property. They also play important roles in biotechnology and food science in the production of various foods, beverages, antibiotics, pharmaceuticals and enzymes.
Some diseases of animals and humans can be caused by moulds, usually as a result of allergic sensitivity to their spores or caused by toxic compounds produced by moulds. The term “toxic mould” refers to moulds that produce mycotoxins, such as Stachybotrys chartarum, and not to all moulds in general. Symptoms caused by mould allergy are watery, itchy eyes, a chronic cough, headaches or migraines, difficulty breathing, rashes, tiredness, sinus problems, nasal blockage and frequent sneezing.
Common household moulds have a characteristic “musty” or “earthy” smell, somewhat like the forest floor deep in the woods. Growing colonies of mould can also be visually observed in many cases. Most people are familiar with mouldy bread or mould growth on cheese or other food products that have been kept too long, so the “green fuzzy” characteristic of most mould growth is familiar.
Mould in the home can usually be found in damp, dark or steamy areas e.g. bathroom or kitchen, cluttered storage areas, recently flooded areas, basement areas, plumbing spaces, areas with poor ventilation and outdoors in humid environments. Moulds are ubiquitous in nature, and mould spores are a common component of household and workplace dust. However, when mould spores are present in large quantities, they can present a health hazard to humans, potentially causing allergic reactions and respiratory problems.
Moulds can also pose a hazard to human and animal health when they are consumed following the growth of certain mould species in stored food. Some species produce toxic secondary metabolites, collectively termed mycotoxins including aflatoxins, ochratoxins, fumonisins, trichotecenes, citrinin, and patulin.
These toxic properties may be used for the benefit of humans when the toxicity is directed against other organisms; for example, penicillin adversely affects the growth of Gram-positive bacteria, clostridia, certain spirochetes, and certain fungi, that cause disease.
How to prevent mould growth
Moulds can grow almost everywhere and on any substance providing moisture is present. Thus, the best method of prevention is to reduce the amount of moisture.
Keep the relative humidity between 30% and 50%. To accomplish this goal, prevention measures include:
- Vent showers and other moisture generating sources directly to the outside.
- Control humidity with air conditioners and/or dehumidifiers (It is important to remember that when using air conditioners and dehumidifiers to keep them in good condition. Empty any water collectors regularly so this water does not contribute to the moisture problem! If you use humidifiers, ensure that they are cleaned regularly).
- Use exhaust fans when cooking, dishwashing, or laundering (especially in the food service or laundry areas) or when cleaning large areas.
- Insulate cold surfaces to prevent condensation on piping, windows, exterior walls, roofs and floors where possible.
- Keep the building and the heating, ventilation and air conditioning (HVAC) systems in good repair.
- Clean up any floods or spills immediately (within 24-48 hours).
- For floors and carpets, remove spots or stains immediately. Reduce the amount of water used when cleaning carpets as much as possible.
- Do not install carpet around fountains, sinks, bathtubs/showers or directly on top of concrete floors that are prone to leaks or frequent condensation.
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